Apparatus for applying a substantially constant tension to an elongated member connected to an installation subject to alternating movements

ABSTRACT

Apparatus for applying a substantially constant tension to an elongated member connected to an installation subjected to alternating movements which comprises the combination of at least one jack supporting said elongated member with regulating means located on the installation, supplying a determined working pressure with the use, as pressure source, of an accumulator delivering to a jack an auxiliary fluid under a pressure varying with the displacement of one element (piston or cylinder) of said jack, comprising at least two jacks, one of which has one element articulated to a fixed point and the other element articulated to one element of another jack through a movable articulation member compelled to be displaced along a predetermined path when one of the elements of a jack is displaced with respect to the other.

United States Patent 1191 Castela et al.

Inventors: Andre Castela, Mesnil-Le-Roi;

Philippe Joubert, Meudon-La-Foret, both of France lnstitut Francais du Petrole, des Carburants et Lubrifiants, Rueil-Malmaison, France Filed: Apr. 28, 1972 Appl. No.: 248,727

Assignee:

Foreign Application Priority Data May 3, 1971 France 7115911 us. 01.; .Q. 60/413, 91/390, 175/5,

254/172 1111.01. FlSb 13/16 Field of Search 60/413, 414, 415; 91/390; 175/5, 7, 27; 254/172 References Cited UNITED STATES PATENTS 12/1964 Reed 60/415 X [45] Jan. 29, 1974 Primary Examiner-Edgar W. Geoghegan Attorney, Agent, or Firm-Craig & Antonelli [5 7] ABSTRACT Apparatus for applying a substantially constant tension to an elongated member connected to an installation subjected to alternating movements which comprises the combination of at least one jack supporting said elongated member with regulating means located on the installation, supplying a determined working pressure with the use, as pressure source, of an accumulator delivering to a jack an auxiliary fluid under a pressure varying with the displacement of one element (piston or cylinder) of said jack, comprising at least two jacks, one of which has one element articulated to a fixed point and the other element articulated to one element of another jack through a movable articulation member compelled to be displaced along a predetermined path when one of the elements of a jack is displaced with respect to the other.

1 Claim, 3 Drawing Figures Pmmimmsm 3788073 SHEET 1 (IF 2 FIG .1

PATENTED A 19M 3.788073 SHEET 2 [IF 2 U l I h APPARATUS FOR APPLYING A SUBSTANTIALLY CONSTANT TENSION TO AN ELONGATED MEMBER CONNECTED TO AN INSTALLATION SUBJECT TO ALTERNATING MOVEMENTS The present invention relates to an apparatus for applying a substantially constant tension to an elongated member connected to an installation subjected to alternating movements.

More particularly, but not limitatively, the invention relates to an apparatus for supporting, with a substantially constant force, an elongated member suspended from an installation subjected to vertical movements.

There will be contemplated, by way of non limitative example, such operations as off-shore drilling operations performed from a floating installation, from which is suspended for example, an elongated member such as a drill string.

During these operations the drill string must be kept under a substantially constant tension, so as to be unaffected by the vertical movements of the floating installation.

The upper end of the drill string is generally connected to a hook carried by a travelling block which is suspended, by a cable used for handling the drill string, from a stationary crown block, located at the top of a derrick carried by the floating installation.

In order to automatically compensate for the vertical movements of the floating installation, it has been proposed to make use of a hydraulic jack fixed at one of its ends to the top of the derrick and supporting the stationary crown block, this jack extending with its longitudinal axis along the direction of displacement of the floating installation, i.e., along a substantially vertical direction. 1

An automatic compensation for the movements of the floating installation is obtained by supplying the jack with fluid under pressure delivered by an oleopneumatic (oil-and-gas) accumulator.

When, as a result of the vertical movements, the piston is displaced within the cylinder of the jack, the pressure in the accumulator varies according to a polytropic law PV K constant It can be shown that, as a first approximation, the volume variations A V and pressure variations A P,, of the mass of gas contained in the accumulator, resulting from the vertical movements of the floating installation, are defined by the relationship A P lP, K A V /V,

In the above formula P is the initial gas pressure in the accumulator which is the same as that of the fluid contained in the jack, whereby a tension force can be exerted on the drill string, V is the volume of the pressurized gas and K a coefficient which depends in particular on the type of gas housed in the accumulator.

For a maximum acceptable variation of 10 percent for example in the tension exerted on the drill string, corresponding to a variation of 10 percent of the pressure in the jack, there must be used an accumulator having a volume V, such that In practice, since the choice of the pressure P, is determined by the design requirements for the accumulator and the jack and by the amplitude of the vertical movement of the floating installation, there must be used accumulators of great volume V,, which are very expensive and bulky on the floating installation.

It has therefore been proposed to add to the vertical jack, one or several inclined jacks, each having one end articulated on the derrick and the other end supporting the stationary crown block. By using such jacks inclined with respect to the travel path of the stationary crown block (path relative to the floating installation) there can be obtained a better regulation in the tension exerted on the drill string and it becomes possible to substantially reduce the overall volume V, of the accumulators. The drawbacks of such devices consist, on

' the one hand, in the fact that the volumes V required suppress or at least to reduce the drawbacks of the prior devices, by providing a device for keeping a working fluid under substantially constant pressure, this device being, in particular, suitable for use in apparatuses for keeping an elongated member under a substantially constant tension.

The apparatus according to the invention, for applying a substantially constant tension to an elongated member connected to an installation subjected to alternating movements, comprises in combination a. means for applying a force to the elongated member, including at least one main jack,

b. regulating means, on the installation, for supplying a working fluid under a determined pressure, this fluid being supplied to said main jack; this regulating means being interposed between the cylinder of said main jack and a source of at least one pressurized fluid, said source containing a gas whose pressure varies with the volume occupied by the gas, this regulating means comprising at least one group of jacks, an element of at least one jack of said group being connected through a moveable articulation to an element of at least another jack of said group the element of at least one jack of said group which is not connected to said moveable articulation being rotatably mounted on a flxed point of the installation, said moveable articulation being compelled to move along a predetermined path, fixed with respect to the installation, said fixed point being so located that the axis of said rotatable jack remains inclined on said path during the rotation of said rotatable jack, at least one jack of said group being fed with pressurized fluid from said source, and at least one jack of said group being connected to the cylinder of said main jack through a pipe containing an incompressible fluid.

One of the advantages of the device according to the invention is to provide an apparatus applying a substantially constant tension to a drill string suspended, through handling means, from the top ofa derrick integral with a mobile installation whose heavy constituting elements are not located at the top of the derrick, so as to improve the stability of the mobile installation.

Other advantages will appear from the following description illustrated by the accompanying drawings, showing a non-limitative embodiment of an apparatus according to the invention for keeping substantially constant the tension exerted on a drill string suspended from an installation for off-shore drilling.

FIG. 1 is an overall view of this apparatus,

FIGS. 2 and 3 respectively show the variation in the pressure applied to the main jack and in the tension ex; erted on the drill column, as a function of the displacements of the piston of this jack, under the action of the vertical movements of the floating installation.

Reference numeral 1 indicates the floating installation topped by a derrick 2. A drill string (not shown) is suspended from the floating installation through handling means constituted, in this particular embodiment, by a hook 3 integral with a travelling block 4 suspended by a cable 5 from a crown block 6. The cable 5, used for handling the drill string, passes over a device, which forms no part of the invention, constituted by articulated arms 7 and 8 and pulleys 9 and 10, for preventing wear of the cable which might result from friction on the crown block.

The crown block 6 is suspended from the end of the stem of a supporting jack l1 fixed to the derrick 2 and constituting the means for supporting the drill string.

This jack is placed substantially in line with the direction of the vertical movements of the floating installation, i.e. along a substantially vertical direction. The jack 1] is connected through a pipe 12 to a regulating device. This device produces a force, in the manner indicated hereinafter, so as to keep under a determined pressure the working fluid supplied to the jack 11.

The elements constituting the regulating device have been shown in a vertical position for the clarity of the drawing, but this arrangement is not limitative. The device comprises a first jack 14 having one of its constituting elements for example its cylinder pivotally articulated at one end thereof about a fixed point 15. A point of its second constituting element, for example the point 18 of the stem of the jack, is compelled to move along a determined path 19, so that the axis of the jack 14 has an inclination angle a along the path 19.

A pipe 20a connects the jack 14 to an accumulator 20 containing an invariable mass of gas. This accumulator 20 is for example an oleopneumatic accumulator whose pressure varies with the relative displacement of the elements constituting the jack 14 when point 18 moves along the path 19.

The path 19 has been so determined that the variations in the inclination a of the jack 14 along the path 19 corresponding to the displacements of the point 18 result in a variation of the ratio of the force exerted by the jack to the component of this force along this path which substantially provides for some compensation of the pressure variations of the fluid in the jack 14.

As a matter of fact, when considering the device in the position shown in the drawing, as the point 18 moves toward the point H of the path 19, the pressure in the jack 14 decreases, thereby producing a corresponding decrease in the force exerted by the jack 14 on the point 18.

Correlatively, the angle or decreases and the component along the path 19 of the force exerted by the jack 14 on the point 18 undergoes relatively small variations.

When the point 18 moves toward the point B of the path 19, the pressure in the jack 14 increases, which results in an increase of the force exerted by the jack 14 on the point 18.

Correlatively the angle a increases and the component along the path 19 of the force exerted by the jack 14 on the point 18 undergoes relatively small variations.

The regulating device is connected to means for converting the component along the path 19 of the force exerted by the jack 14 into a determined pressure P These converting means consist of an intermediate jack 16, whose constituting elements, for example the stem of the jack 16, is connected to the point 18, the other constituting element, for example the cylinder of the jack 16, being integral with a fixed supporting point 17.

In the drawing the cylinder of the jack 16 is articulated about its fixed supporting point 17 and the axis of the jack 16 makes an angle B with the path 19, this angle B varying with the displacements of the point 18 on the path 19.

It will be obviously possible, without departingfrom the scope of the invention, to place the jack 16 with its axis along the path 19.

By this way, the stem of the jack 16 is subjected to the action of the component along the path 19, of the force exerted by the jack 14, which maintains under a determined pressure the fluid which is contained in the jack l6 and conveyed to the supporting jack 11 through the pipe 12.

The pressure P supplied by the jack 16 and the pressure P in the accumulator 20 are interrelated through the relationship P P(S/S) (Cosoz/Cos B) The values of this pressure which correspond to the limit positions (B and H) of the moveable articulation 18 in the guideway 19 (FIG. 1) are respectively n P8 /S) a/ 8) and Pu P (COSa /COS B wherein the indexes B and H indicate the particular values of the different parameters Pu, P, a and B of the relation (1), corresponding to the respective positions B and H of the moveable articulation 18.

In practice, it is sufficient to choose the limit values Pu and Pu of the desired working pressure Pu which has to be supplied by the jack 11 for the limit positions of the moveable element of the jack 11 (these values Pu and Fu being, or not, different).

The values Pu,, and Pu will be selected as a function of the particular conditions of each considered case of utilization.

In the contemplated embodiment wherein this pressure is used in a main or supporting jack 11 in order to control the tension T applied to a drill column, the values of Pu and Pu will for example be determined with consideration of the influence of a system of pulleys interposed between the drill column and the supporting jack 11.

Test values are selected for the construction parameters of the regulating system, these parameters being (FIG. 1) the values of d and d (respective distances of the articulation points 15 and 17 from the axis of the guideway 19), the limit values a a and B B,, of the angles a and B and the values of the respective crosssections S and S of the jacks l4 and 16 respectively.

By application of the relationships (2) and (3) it can be deduced from the values selected for Pu, and Pu the values P and P of the pressure of the auxiliary fluid in the accumulator 20, as a function of the values a a B and 8,, (FIG. 1) which have been selected.

The determination of the values of P and P makes it possible to calculate the volume which is necessary for the accumulator 20.

As a matter of fact, the pressure P in this accumulator varies substantially according to a physical law having the form' PV" constant, wherein K is a coefficient whose value depends, in particular, on the nature of the pressurized gas and V is the volume of gas at the pressure P of the accumulator 20, applied to the piston of the jack 14.

There results therefrom the relationship PIIVIIK n n wherein V and V are the values of the volume of pressurized gas when the position of the moveable articulation 18 is respectively at point B and point H of the guideway 19. v

Letting V V,, be defined as AV there results from the relation (5) The value of A V is known, since it is equal to the product of the cross-section S of the jack 14 by the stroke of its piston when the moveable articulation 18 is displaced between points B and H, V being the minimum value of the volume of pressurized gas.

The nominal volume of the accumulator can thus be determined since the values of P and P have already been determined (the calibrating pressure of this accumulator is substantially equal to P Thereafter can be plotted, in the manner to be indicated hereinunder, the curve T=F(h) representing the variations in the tension T applied to the drill column, as a function of the displacement h of the main jack 11 from its lowermost position.

To each value of h corresponds a well defined position of the moveable articulation 18 along the guideway ilie well defined values for the angles a and B, when the values [3 [3B, dm and S have been fixed.

Asa mattr of fact, to the displacement h of the piston of jack 11 from its lowermost position corresponds a determined variation of the volume of hydraulic fluid in the cylinder of jack [6 through the pipe 12 (at any moment the displacements of the pistons of the jacks 11 and 16 from their initial position (lowest osition), represent the same percentage of their maximal stroke).

In this position of the moveable articulation 18, to

' 'Ph PiS/S (Gosh/Cos and there is deduced the-corresponding va'ifi'dr the tension T which, in the embodiment illustrated by way of example, depends on the influence of the pulley or block system.

The graphs of FIGS. 2 and 3 show respectively the variations of Pu (expressed in kg/cm and T (expressed in tons), as a function of the stroke h (expressed in meters) of the piston ofjack 11, obtained in accordance with the following data horizontal distance between the axes of pulleys 9 and 10 and the axis of pulley 6 when the latter is in its lowermost position 3.3 meters,

vertical distance between the axes of pulleys 9 and 10 and the axis of pulley 6 when the latter is in its lowermost position 1.8 meters,

The cable 5 forms 12 turns between the pulley 6 and the moveable block or pulley system 4.

maximum stroke h (FIG. 1) of the main jack 11 determined by the amplitude of the vertical movements of the floating installation 4.6 meters.

Moreover the following data have been selected d 3.30 meters d 3.90 meters In the graphs of FIGS. 2 and 3 the curves in dotted lines show the varations obtained for Pu and T respectively when choosing The curves in solid lines show the results which are obtained with the following newly selected values 1 It is thus possible to optimize the system by selecting for the parameters of construction i ,8 (1 4, S and fi B d and S, the values corresponding to the test curve of the pressure Pu which is nearer the curve in clot and dash line representing the desired values of this pressure Pu, 15 this particular embodiment, chosen in order to obtain the variations of the force exerted by the jack 11 which makes it possible to keep substantially constant the tension T applied to the drill column.

It should be noted that on the graph of FIG. 3 the scale of the ordinates has been considerably amplified, the relative variations in the tension T of the drill column not exceeding 1 1.5 percent.

' It will obviously be possible to select differently the limit values Pu and Pu of the pressure, to comply with different conditions of use and for example as a consequence of a different value of the tension T.

This can be achieved by a modification of the mass of fluid in the accumulator 20, for example by actuating on the valve 20b (FIG. 1).

What we claim is I. An apparatus for applying a substantially constant element of at least another jack of said group, at least one jack of said group having one element not connected to said moveable articulation and rotatably mounted on a fixed point of the installation,

tension to an elongated member connected to an installation subjected to alternating movements, which comprises a combination:

a. means for applying a force to the elongated member, including at least one main jack, said moveable articulation being compelled to b. regulating means on the installation, for supplying move along a predetermined path, fixed with rea substantially incompressible working fluid under spect to the installation, said fixed point being so a determined pressure, this fluid being supplied to located that the axis of said jack having a rotatably said main jack, this regulating means being intermounted element remains inclined on said path posed between the cylinder of said main jack and 10 during rotation of said jack having a rotatably a source of at least one pressurized fluid, said mounted element, at least one jack of said group source containing a gas whose pressure varies with being fed with fluid at the pressure of said source, the volume occupied by the gas, this regulating and at least one jack of said group su plying the means comprising at least one group of jacks, an cylinder of said main jack with said incompressible element of at least one jack of said group being fluid at a determined pressure different from that connected through a moveable articulation to an of the source through a pipe.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 8 073 Dated January 29, 1974 Andre Castela and Philippe Joubert It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 4, equations (1), (2) and (3) should readas followsz.

Pu P (s/S) (Cos a/Cosfi) H1 P (s/S) (Cosa /Cos (S Pu P (s/S) (Cos o /Cos B (3) In column 5, line 2 should read:

sections sand S of the jacks 14 and 16 respectively.

In column 5, line 342 should read:

product of the cross-section s of the jack 14 by the Page 1 of? UNITED STATES PATENT OFFICE l CERTIFICATE OF CORRECTION Patent No 073 Dated January 29, 1974 Inventor) I Andre Castela and Philippe Joubert It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

CONTINUED In column 5, lines 66 and 67, the equations should read:

hence P P B IV (V VH In colunm 6; the equation in line 8' should read:

Pu P.(S/S) (Cos a/Cos [3) In column 6, line 47' should read:

for the parameters of construction 0 B (1 s and Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. (3.. MARSHALL DANN Attesting Officer Commissioner of Patents Page 2 of 2 

1. An apparatus for applying a substantially constant tension to an elongated member connected to an installation subjected to alternating movements, which comprises a combination: a. means for applying a force to the elongated member, including at least one main jack, b. regulating means on the installation, for supplying a substantially incompressible working fluid under a determined pressure, this fluid being supplied to said main jack, this regulating means being interposed between the cylinder of said main jack and a source of at least one pressurized fluid, said source containing a gas whose pressure varies with the volume occupied by the gas, this regulating means comprising at least one group of jacks, an element of at least one jack of said group being connected through a moveable articulation to an element of at least another jack of said group, at least one jack of said group having one element not connected to said moveable articulation and rotatably mounted on a fixed point of the installation, said moveable articulation being compelled to move along a predetermined path, fixed with respect to the installation, said fixed point being so located that the axis of said jack having a rotatably mounted element remains inclined on said path during rotation of said jack having a rotatably mounted element, at least one jack of said group being fed with fluid at the pressure of said source, and at least one jack of said group supplying the cylinder of said main jack with said incompressible fluid at a determined pressure different from that of the source through a pipe. 